Why do movie keys use blue cloth or green cloth as the background?

Film shooting usually uses blue cloth or green cloth as the background, because in post-production, the silhouette of the specified color looks "transparent" and a specific background or animation is inserted in the "transparent" area.

In theory, any color can use this function, and blue and green are not required. The higher the color purity, the more convenient it is to key the image. We use these two colors because we seldom use them in our daily life. Imagine if we use black as the background color, then the black clothes, black hair and even black eyes on the characters will be removed in the post-processing.

So when we choose colors, we will choose the color with the lowest usage rate or appearance rate. China generally uses blue more, while European and American countries use green more. Because some Europeans and Americans have blue eyes, they don't use blue.

Extended data:

Keying is a common method in film and television production, which is widely used in film and television industry, such as special effects, background production and so on! For example, most of the background of the talk show is the result of the later period.

Keying usually adopts two ways: "digging blue" and "digging green". Blue-cutting technology refers to the technology of shooting with blue as the background when shooting or taking pictures, and using the "color key" of stunt machine to cut off the blue background and replace it with other more ideal backgrounds in post-production to make actors and props look like shooting in other more ideal backgrounds.

In order to achieve the purpose of digging blue, actors and props are required not to use blue when shooting. The blue background requires uniform light, and there can be no shadows and chromatic aberration. In order to achieve the purpose of changing the background, in addition to digging blue, it is often "digging green", that is, shooting with a green background. Whether digging blue or green, it is usually done in the studio, because only the studio can arrange the light as evenly as possible. This kind of studio dedicated to digging blue is called "blue box" in the industry.